docs: def ipv6_is_defined(address):
      """
      The function for checking if an IPv6 address is defined (does not need to
      be resolved).
  
      Args:
          address (:obj:`str`): An IPv6 address.
  
      Returns:
          namedtuple:
  
          :is_defined (bool): True if given address is defined, otherwise
              False
          :ietf_name (str): IETF assignment name if given address is
              defined, otherwise ''
          :ietf_rfc (str): IETF assignment RFC if given address is defined,
              otherwise ''
      """
  
      # Initialize the IP address object.
      query_ip = IPv6Address(str(address))
  
      # Initialize the results named tuple
      results = namedtuple('ipv6_is_defined_results', 'is_defined, ietf_name, '
                                                      'ietf_rfc')
      # Multicast
      if query_ip.is_multicast:
  
          return results(True, 'Multicast', 'RFC 4291, Section 2.7')
  
      # Unspecified
      elif query_ip.is_unspecified:
  
          return results(True, 'Unspecified', 'RFC 4291, Section 2.5.2')
  
      # Loopback.
      elif query_ip.is_loopback:
  
          return results(True, 'Loopback', 'RFC 4291, Section 2.5.3')
  
      # Reserved
      elif query_ip.is_reserved:
  
          return results(True, 'Reserved', 'RFC 4291')
  
      # Link-Local
      elif query_ip.is_link_local:
  
          return results(True, 'Link-Local', 'RFC 4291, Section 2.5.6')
  
      # Site-Local
      elif query_ip.is_site_local:
  
          return results(True, 'Site-Local', 'RFC 4291, Section 2.5.7')
  
      # Unique Local Unicast
      elif query_ip.is_private:
  
          return results(True, 'Unique Local Unicast', 'RFC 4193')
  
      return results(False, '', '')